1. Field of the Invention
The invention relates to signal processing of multiple channels.
2. Description of the Background Art
Conventionally, signal processing apparatuses that extract a specific component from an input signal, that identify a source of the signal based on the component extracted, that change the component extracted from the input signal and that output the component changed, are known.
For example, when extracting the specific component from the input signal, the signal processing apparatuses transform the input signal by using one of transformation methods of Fourier transform and Hilbert transform. Signal processing apparatuses that generate an output signal based on the signal transformed have been disclosed. Here, the signal transformed is, for example, a signal that consists of a real part and an imaginary part.
When using Fast Fourier Transform (FFT) for signal transformation, it is required to save the input signal to a storage area (hereinafter referred to as a “buffer”) for every input signal having a predetermined length. On the other hand, when using Hilbert transform for the signal transformation processing, it is not required to save the input signal in the buffer but it is possible to process the input signals serially. Therefore, a processing load is lower and a tracking capability of signal processing to follow a change of the input signal can be improved when the signal processing apparatus performs the signal processing, by using Hilbert transform, as compared to by using Fourier transform.
However, when the signal processing apparatus generates the output signal based on the input signal, there is a case where the output signal contains noise in the signal processing by using Hilbert transform.
For example, in a case where an input signal is an acoustic signal, when a conventional signal processing apparatus performs processing that reduces a correlation component (hereinafter referred to also as a “center component”) that is common in each of acoustic signals for multiple channels, by using Hilbert transform, the tracking capability of signal processing to follow a change of the acoustic signal can be improved. Here, the center component is a component localized in the proximity to a center between a right speaker and a left speaker. For example, in a case of a piece of music that includes a vocal and a musical accompaniment, the vocal corresponds to the center component.
However, because of high tracking capability of signal processing to follow a change of the acoustic signal, the rate of the center component of the acoustic signal may change rapidly. Since the signal processing apparatus performs the processing that reduces the center component changing rapidly, noise may be contained in an output signal. As a result, a user will hear output sound containing strong noise.